Megalithic seems more fitting than cyclopean to me.

I’ve seen “cyclopean” (lower case) used to mean “huge” in fiction a few times, especially in fiction set in the past.

Interestingly, this dictionary lists three meanings of the word: https://www.thefreedictionary.com/cyclopean

The first is “referring to a Cyclops”. The second is “huge”. The third is in reference to these types of (megalithic) ruins.

I wonder if the first meaning is the original one, and the others evolved from that meaning as our understanding of human history changed.